A small butane gas stove carried aboard by a Moslem pilgrim may have started the fire, according to a communique issued by the Saudi aviation authority and broadcast by the state radio. The statement said inspectors found two such stoves in the passenger compartment and a fire extinguisher was found near one of them.

Earlier, investigators said they suspected a short circuit in the cockpit. It was still unclear, however, why the plane's emergency doors could not be opened, and Saudi officials said an investigation of the accident would be launched with Lockheed officials.

Saudi aviation officials said some passengers were found jammed against the exit-doors, apparently preventing them from opening. Lockheed officials in California were quoted as expressing surprise at reports that the doors might have malfunctioned, since the Tristar has 11 independently operated emergency exits.

Earlier accounts of the tragedy, citing passenger lists, put the death toll at 265, which included 16 crew members. The Tristar was on a flight yesterday from Karachi, Pakistan, to Riyadh and then on to Jeddah, the Saudi Red Sea port 500 miles west of here.

The pilot was forced to turn back shortly after takeoff from Riyadh, however, when fire was discovered aboard the aircraft.After the plane made an emergency landing, it appeared to explode into flames.

There were conflicting reports about the nationalities of the passengers, although it was clear that a majority were Saudis. About a quarter were believed to be Pakistanis, and as many as 30 may have been Iranians. Various reports said there were several South Koreans, Britons, Filipinos, Bangladeshis, Egyptians and Sudanese aboard as well.

It was unclear how many of the passengers were American, but an airline spokesman in London said a flight engineer named W. Curtis died in the aircraft, and other airline representatives in Karachi identified as American passengers Donald Kot, Stephen Kot and A. Ghafoor Shafi.

[The Muskegon Bank and Trust Co. of Muskegon, Mich., said it was notified that William Willett, 53, formerly of Muskegon, was aboard the plane. The bank holds a trust for Willett, who worked for a Boston-based construction company.]

The toll from the accident was so high, officials said, because firefighters and rescue workers were unable to open the plane's doors. "As the tongues of flame shot out the windows of the plane, it became impossible to open the doors from the outside or inside," a statement from the Saudi Directorate of Civil Aviation said.

"The whole plane was engulfed in flames."

As the aircraft approached for the emergency landing, the Saudi radio report said, fire brigades and ambulances were rushed to the runway and rescue helicopters took to the air. A "fierce glow of fire" could be seen.

The pilot told the control tower he was trying to rush his 285 passengers to safety through the emergency chutes, the report continued, but radio contact was cut and the body of the plane became wrapped in flames.

The airport compound was guarded by security officers today, while a team of experts began the investigation to determine the cause of the fire. Reporters were barred from the area.

King Khalid of Saudi Arabia ordered $15,000 be paid to the families of each of the 301 victims, the Saudi press agency said. The total payment would come to $4,515,000.

A royal statement quoted by the agency said that "in expression of Khalid's deep condolences to the families of the victims and his majesty's wish to each their grief," the king ordered the payments.

The worst accident in aviation history occurred on Tenerife in the Spanish Canary Islands in March 1977, when 582 persons were killed in the collision on a runway of two Boeing 747s operated by Pan American Airways and the Dutch airline KLM.

The second worst, and the greatest loss of life in a single-plane accident, was the crash of a Turkish Airlines DC10 northeast of Paris in March 1974 in which 346 people perished.

The crash of an American Airlines DC10 in Chicago in May 1979 killed 273 persons.